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<head>

  <meta charset="utf-8">

  <title>Global test()</title>

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<body>

  <h1>lastIndex pitfall</h1>

  <pre id="out"></pre>

  <script>

    var regex = /a/g;

    var out = "";

    out += "call 1: " + regex.test("aba") + "\n";

    out += "call 2: " + regex.test("aba") + "\n";

    out += "call 3: " + regex.test("aba") + "\n";

    regex.lastIndex = 0;

    out += "after reset: " + regex.test("aba");

    document.getElementById("out").textContent = out;

  </script>

</body>

</html>

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JavaScript RegExp test() — global lastIndex (Try It)